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Aqueous stream characterization from biomass fast pyrolysis and catalytic fast pyrolysis Brenna A. Black, William E. Michener, Kelsey J. Ramirez, Mary J. Biddy, Brandon C Knott, Mark William Jarvis, Jessica Olstad, Ofei D. Mante, David C. Dayton, and Gregg T Beckham ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b01766 • Publication Date (Web): 05 Sep 2016 Downloaded from http://pubs.acs.org on September 11, 2016

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ACS Sustainable Chemistry & Engineering

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Aqueous stream characterization from biomass

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fast pyrolysis and catalytic fast pyrolysis

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Brenna A. Black†, William E. Michener†, Kelsey J. Ramirez†, Mary J. Biddy†, Brandon C. Knott†,

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Mark W. Jarvis†, Jessica Olstad†, Ofei D. Mante‡, David C. Dayton‡, and Gregg T. Beckham†, *

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†

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Parkway, Golden CO 80401 USA

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‡

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Park NC 27709 USA

National Bioenergy Center, National Renewable Energy Laboratory, 15013 Denver West

Energy Technologies Division, RTI International, 3040 E. Cornwallis Road, Research Triangle

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*

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Gregg T. Beckham

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Email: [email protected]

Corresponding author footnote:

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Key words

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Pyrolysis, Reforming, Wastewater, Biomass conversion, Biorefinery, Thermochemical

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Conversion

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ACS Paragon Plus Environment

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Abstract

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Biomass pyrolysis offers a promising means to rapidly depolymerize lignocellulosic biomass for

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subsequent catalytic upgrading to renewable fuels. Substantial efforts are currently ongoing to

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optimize pyrolysis processes including various fast pyrolysis and catalytic fast pyrolysis

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schemes. In all cases, complex aqueous streams are generated containing solubilized organic

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compounds that are not converted to target fuels or chemicals, and are often slated for

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wastewater treatment, in turn creating an economic burden on the biorefinery. Valorization of the

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species in these aqueous streams, however, offers significant potential for substantially

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improving the economics and sustainability of thermochemical biorefineries. To that end, here

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we provide a thorough characterization of the aqueous streams from four pilot-scale pyrolysis

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processes: namely, from fast pyrolysis, fast pyrolysis with downstream fractionation, in situ

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catalytic fast pyrolysis, and ex situ catalytic fast pyrolysis. These configurations and processes

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represent characteristic pyrolysis processes undergoing intense development currently. Using a

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comprehensive suite of aqueous-compatible analytical techniques, we quantitatively characterize

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between 12 g kg-1 organic carbon of a highly aqueous catalytic fast pyrolysis stream and up to

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315 g kg-1 organic carbon present in the fast pyrolysis aqueous streams. In all cases, the analysis

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ranges between 75-100% of mass closure. The composition and stream properties closely match

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the nature of pyrolysis processes, with high contents of carbohydrate-derived compounds in the

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fast pyrolysis aqueous phase, high acid content in nearly all streams, and mostly recalcitrant

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phenolics in the heavily deoxygenated ex situ catalytic fast pyrolysis stream. Overall, this work

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provides a detailed compositional analysis of aqueous streams from leading thermochemical

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processes – analyses that are critical for subsequent development of selective valorization

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strategies for these current waste streams.


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Introduction

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Biomass pyrolysis is a promising high-temperature conversion approach to deconstruct

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lignocellulosic substrates to intermediates for upgrading to drop-in hydrocarbon fuels, or

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potentially to aromatic chemicals.1–3 However, multiple challenges remain to fully realize the

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cost-effective potential of biomass pyrolysis at the industrial scale.4,5 As such, multiple process

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configurations are being developed in parallel to address these challenges, which mostly differ in

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the means by which they deal with the pyrolysis products and where and how chemical catalysis

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is applied. In virtually all cases, biomass pyrolysis processes (and other high-temperature

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conversion processes such as hydrothermal liquefaction) reject a fraction of biomass carbon to

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the aqueous phase, creating a potentially costly wastewater treatment burden for thermochemical

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biorefineries. Emerging strategies to upgrade the aqueous fractions originating from

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thermochemical processing include aqueous-phase reforming to produce hydrogen for use in the

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biorefinery, catalytic hydrothermal gasification to produce fuel- or synthesis-gas, or fractionation

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and selective upgrading of components rejected to the aqueous stream.3,6 The two former

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strategies often require a significant process heat burden and the latter potentially costly

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separations depending on the target molecules and intended applications. Regardless, treating the

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aqueous streams as only wastewater represents a potentially significant carbon loss and high

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cost, relative to a potential revenue stream in a more holistic, efficient biorefinery scheme.

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Developing robust strategies to valorize the aqueous fractions from thermochemical processing

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will, however, undoubtedly need to be designed closely with the pyrolysis process scheme, and

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the composition of the aqueous fractions will need to be thoroughly characterized.

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Subsequent to biomass fast pyrolysis (FP), bio-oil can be fractionated via multiple strategies.

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Bio-oil can be partitioned through the addition of water, (mass ratios as high as 9:1 water-to-oil

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have been reported)7 creating a bio-oil and a carbon-rich aqueous phase containing a substantial

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amount of polysaccharide-derived compounds; the organic phase is typically hydrotreated and

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the aqueous fraction slated for wastewater treatment, thus representing a carbon loss for FP

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processes.1,8,10 Past work on characterizing the aqueous fraction produced via FP has utilized gas

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chromatography-flame ionization detection (GC-FID), gas chromatography- mass spectrometry

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(GC-MS), and high performance liquid chromatography (HPLC), where mass and carbon

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closures have generally not exceeded 60 wt%. The most prevalent compounds identified in FP

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aqueous streams are levoglucosan, 1-hydroxypropan-2-one (hydroxyacetone or acetol), acetic

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acid,

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(furfural).7,10–12 Brown et al. developed a strategy to overcome this carbon loss in FP via the use

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of a multistage separation strategy that combines condensers and electrostatic precipitation

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through “stage fractions” to produce up to 5 streams from FP of tunable composition, including

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an aqueous-rich stream with a high content of light oxygenates (Stage Fraction 5, SF5).13

2-hydroxyacetaldehyde,

benzene-1,2-diol

(catechol),

and

furan-2-carbaldehyde

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Conversely to FP, catalytic fast pyrolysis (CFP) has emerged as another promising biomass

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conversion approach. In particular, in situ CFP is conducted by mixing biomass and a catalyst

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together before pyrolysis, and partial deoxygenation occurs via dehydration, decarboxylation,

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and decarbonylation during the thermal deconstruction of biomass. Thus the water yield is

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increased in CFP relative to FP, as a sizable fraction of the biomass carbon can become

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solubilized in the aqueous phase.15 Ex situ CFP, on the other hand, passes pyrolysis vapors over

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metal, or metal free micro- and meso-porous zeolite catalysts for partial deoxygenation, thus


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physically separating the catalyst and solid biomass.15 Chemical characterization of CFP aqueous

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phase is limited, and if available is not detailed adequately for upgrading potential. Paasikallio et

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al. reported the composition of a solvent fractionated in situ CFP process as broad classes of

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compounds, such as “acids, aldehydes, ketones, alcohols, phenols” (11 wt%), and “sugar-type

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compounds” (22 wt%).16

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Each of these described pyrolysis processes are undergoing development at the pilot scale, and

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rigorous techno-economic and life-cycle analyses are being conducted to identify key cost

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drivers in these processes.17,18 In all cases, aqueous streams are produced, which to date have not

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been thoroughly characterized. To that end, here we employ a wide range of analytical methods,

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including aqueous based gel permeation chromatography (GPC), liquid chromatography - mass

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spectrometry (LC-MS), GC-MS, ultimate analysis, elemental analysis, and physicochemical

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measurements to fully characterize the aqueous fractions from five process streams (Figure 1).

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These streams include the aqueous fractions from FP, FP with fractionation from Iowa State

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University (ISU), two in situ CFP streams from RTI International, and one ex situ CFP stream

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from the National Renewable Energy Laboratory (NREL). The results highlight a broad range of

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compositions and chemical functionality with a strong dependence on the pyrolysis process and

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feedstock. Overall, these results will inform the development of selective valorization strategies

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of pyrolysis-derived aqueous streams based on thermal, catalytic, or biological approaches.

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Figure 1. Simplified process flow diagram of FP and CFP tracking aqueous streams collected for

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compositional and chemical characterization.13,19,20

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Materials and Methods

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Vapor phase upgrading system

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To produce the CFPNREL stream, the Vapor Phase Upgrading system was used, which comprises

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two separate units, the pyrolysis reactor and the Davison Circulating Riser (DCR), both of which

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can be operated independently when not integrated (Figure 2). The pyrolysis system consisted of

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a 2” fluidized bed reactor (500°C, 25 psig, 1.5 s) with dual stage cyclonic char removal and hot

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gas filtration (400°C) to provide char free pyrolysis vapor in nitrogen to the DCR (1 kg hr-1

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total). A mixture of hardwood (red and white oak) biomass was fed into the system at a rate of


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1.75 kg hr-1 with 3.5 kg hr-1 of nitrogen for fluidization, for a biomass to nitrogen ratio of 0.5.

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The primary flow of vapors was condensed in a spray tower with dodecane at 25°C and

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separated from the quench fluid in a horizontal phase separator. A slipstream of the hot pyrolysis

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products was monitored via molecular beam mass spectrometry and the permanent gases via

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nondispersive infrared (NDIR) detection (CO2, CO, CH4).

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Catalytic upgrading of the pyrolysis vapor was conducted in the DCR. The DCR was operated

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adiabatically, similar to industrial fluid catalytic cracking (FCC) units. During DCR operation,

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the system was operated at a pressure of 20 psig, a riser temperature of 550°C, and a pyrolysis

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vapor feed rate of 1 kg hr-1. The catalyst circulation rate (the source of heat to the riser) varies to

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maintain the desired target temperatures. Product was removed from the catalyst via stripping

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(500°C, steam rate of 30 ml hr-1). Air was introduced into the regenerator (600°C) for in situ

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catalyst regeneration, and the resulting flue gas was analyzed via NDIR (CO and CO2) to

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determine coke deposition on the catalyst. The post-stripper product stream, which was

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composed of nitrogen, steam, and hydrocarbons, was sent through a reflux condenser that uses a

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countercurrent flow of cold product liquids to scrub the product gases. The condensed product

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was allowed to drain and separates into a hydrocarbon phase and an aqueous phase. Residual

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product gases were analyzed via GC. For the current work, fresh ZSM-5 catalyst (containing

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FCC additive, 1.8 kg) was used to upgrade the pyrolysis vapors, with a catalyst to biomass ratio

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of 12.9. The resulting aqueous phase was collected and analyzed. It is important to note that,

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although the direct relationship was not studied in this work, the process conditions of CFP, such

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as the catalyst to biomass ratio, directly affect the quality and quantity of the aqueous stream,

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which will be reported in a future study.


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Figure 2. Schematic of the integrated pyrolysis and DCR units

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Aqueous phase sample collection

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Production of FP aqueous samples at NREL was conducted in a pilot-scale system by pyrolyzing

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white oak particles (Quercus alba) (Country Boy, Gamaliel, KY) at 500°C in an entrained flow

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reactor with a nitrogen carrier gas, as similar to the setup described previously without hot gas

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filtration.19 The aqueous fraction of the oil was made using a 1 HP high shear lab mixer with a

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3.5 cm dispersing head in batch mixing mode (Model ME 100LC, Charles Ross and Sons Co.,

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Hauggauge, NY). The mixer was operated at 3300 rpm while 200 g min-1 pyrolysis oil was added

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to deionized water for a final ratio of water/oil (2:1, w/w), and mixed for an additional 10 min.

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After allowing the bulk material to phase separate, the upper aqueous phase was decanted,

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collected and characterized.

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The aqueous fraction of fast pyrolysis from ISU was produced using red oak biomass (Quercus

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rubra) (Wood Residual Solutions LLC, Montello, WI), as previously described.13 Briefly, the

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biomass was fed into a fluidized bed pyrolysis reactor (8 kg h-1 process development unit) with a

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five-stage recovery system. The biomass was pyrolized at 500°C and fluidized with nitrogen in

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the reactor prior to stage fractionation. The fifth and final fraction designed to remove water and

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light oxygenate compounds was collected and characterized.

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A pilot-scale, 1 tonne per day, circulating fluidized bed reactor system was used for the CFP of

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both loblolly pine (Pinus taeda) and white oak feedstock by RTI International, as described

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previously.20 Briefly, biomass was continuously fed into an entrained reactor system with

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fluidizing nitrogen, into which, the catalyst was also circulated into the mixing zone and

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pyrolysis reactions occurred between approximately 450-500°C, 20-30 psi at a residence time of

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0.5 – 1 min. Aqueous products were collected after condensation of pyrolysis vapors in the

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quench system. The quench products were allowed to settle and phase separate over time, after

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which the aqueous phase was collected and characterized.

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The ultimate and proximate compositional analyses of all woody feedstocks used in this study

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are presented in Table 1. All samples have lower ash contents and the compositions are typical

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to that of woody biomass.21

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Table 1. Biomass composition in dry weight basis (wt%) Fast Pyrolysis Catalytic Fast Pyrolysis CFPRTI-pine18 CFPRTI-oak CFP NREL-oak FPNREL-oak17 SF5ISU-oak11 Properties ex-situ in-situ in-situ 48.6 46.4 49.7 46.0 48.7 Carbon 5.1 6.4 6.6 6.0 6.6 Hydrogen 0.1 0.1 0.1 0.5 0.5 Nitrogen 39.9 46.8 43.3 47.0 44.2 Oxygen* 5.8 4.8 3.6 10.6 10.1 Moisture** 0.5 0.3 0.4 0.6 0.4 Ash 79.1 NR 88.6 82.5 82.8 Volatile carbon 14.6 NR 11.0 17.2 16.8 Fixed carbon *Calculated by difference of CHN and ash; **as received; NR = not reported

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Compositional analysis

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Approximately 30 mg aliquots of aqueous fractions were analyzed for water content using Karl

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Fisher titration according to the standard ASTM E203-08. The analysis was performed using a

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Metrome 701 Titrino titration system using methanol as a solvent and Hydranal®-Composite 5

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reagent (Sigma Aldrich, St. Louis, MO) as the titrant, which was standardized against a National

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Institute of Standards and Technology traceable water standard prior to titration. TOC analysis

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was measured by a Shimadzu TOC-LCSH analyzer (Shimadzu, Columbia, MD) via a combustion

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catalytic oxidation method after sample acidification by concentrated hydrochloric acid. COD

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measurements were performed following a digestion with the addition of an acidified dichromate

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solution (Hach COD Digestion Vials, high range) for two hours at 150°C. The resulting material

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was measured for the reduction of the dichromate ion (Cr2O72-) into a green chromic ion (Cr3+) at

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620 nm using a DR600 Benchtop spectrometer (Hach, Loveland, CO). Ultimate analysis was

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performed via high temperature combustion using a LECO TruSpec module (LECO Corp., St.

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Joseph, MI) for carbon, hydrogen, and nitrogen with oxygen by difference. Approximately 100

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mg of each sample was combusted at 950°C under a flow of oxygen for 200 sec. The gas


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produced during combustion was collected and analyzed using infrared spectroscopy to calculate

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hydrogen and carbon content. After which, the gas was scrubbed and reduced to calculate

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nitrogen via the change in thermal conductivity. Ethylenediaminetetraacetic acid (EDTA) was

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used as standard for CHN determination and to assess drift. Inductively coupled plasma atomic

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emission spectroscopy (ICP-AES) was performed following a concentrated nitric acid digestion

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of samples at a concentration of 0.05 g mL-1 with a microwave oven temperature gradient of

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23°C to 150°C over 10 min and then held constant at 150°C for an additional 10 min. Aluminum

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(Al), calcium (Ca), chromium (Cr), copper (Cu), iron (Fe), potassium (K), magnesium (Mg),

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manages (Mn), sodium (Na), nickel (Ni), phosphorus (P), sulfur (S), and zinc (Zn) measurements

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were performed using a Spectro Arcos ICP analyzer monitoring elemental emission lines in the

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range of 130 to 773 nm (Spectro Analytical Instruments Inc., Kleve, Germany). All lines were

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acquired at 1425 W plasma. The instrument was calibrated with commercial standards and

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samples were run in nine independent measurements (n=9). Determination of carbonyl groups

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was done using potentiometric titration with triethanolamine using 0.1 g sample, as outlined

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previously.22 Total acid number (TAN) was determined similarly to an adjusted solvent method23

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from that of ASTM D664, using a Metrohm 842 Titrando automatic titrator (Metrohm,

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Riverview, FL) for potentiometric titrations. A 4:1 ethanol/water (v/v) solution was added at 40

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mL to each 0.5 – 0.8 g aqueous sample and titrated to a pH of 13 with standardized 50 mM

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sodium hydroxide in water. The sodium hydroxide solution was standardized with potassium

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hydrogen phthalate, and carboxylic acids of known concentration were used to ensure validity of

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the method. Compositional evaluation of pyrolysis aqueous streams was measured in triplicate

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analysis unless otherwise stated.

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Aqueous gel permeation chromatography analysis

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Molecular weight distribution was performed using an HPLC Agilent 1260 Infinity series,

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including a refractive index detector (RID) (Agilent Technologies, Santa Clara, CA). Samples

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were injected at a 10-fold dilution at 20 µL onto a TSKgel Alpha column (7 µm, 7.8 mm i.d. ×

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300 mm). Analytes were separated using an isocratic flow of 40 mM LiBr in water/methanol

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(1:1, v/v) at a flow rate of 0.5 mL min-1. A temperature of 55°C was maintained for both the

228

column and the RID. Data from the RID was processed using Cirrus GPC software version 3.4.1

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(Agilent Technologies, Santa Clara, CA). The software was calibrated using 8K and 3K

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polyethylene glycol standards, as well as acetic acid, glucose, xylobiose, xylotriose, and

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xylotetraose. Masses were also confirmed by coupling the GPC chromatography to an Ion Trap

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mass spectrometer monitoring masses between 40 – 2200 Da with mass parameters as described

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subsequently.

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High resolution infusion-tandem mass spectral analysis

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Infusion-mass analysis was performed for initial identification of residual water-soluble analytes.

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Samples were diluted 1000-fold in a solvent mixture of methanol/isopropyl alcohol (3:1, v/v);

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additionally, to ensure the ionization of analytes, a modifier of either 25 mM ammonium

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hydroxide or 4 mM ammonium formate was added to each mixture. Sample solutions were

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directly infused at 10 µL min-1 into a Waters Micromass Q-Tof micro™ with MassLynx™ V4.1

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software (Waters Corp., Milford, MA). External and internal calibration of the mass analyzer

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was implemented to provide a mass measurement accuracy of less than five parts-per-million

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facilitating elemental composition assignment. To ensure mass accuracy of the mass

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spectrometer, a LockSpray™ interface was used to infuse a concentration of 20 pmol µL-1


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glucose in methanol/water (1:1, v/v) with either 4 mM ammonium acetate (negative-ion mode)

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or sodium chloride (positive-ion mode) was infused at a flow rate of 0.2 µL min-1. The frequency

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of the LockSpray™ was set at 10 sec and averaged over 10 spectra to provide an in-line

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correction factor.

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Positive- and negative-ion ESI/MS and tandem mass spectrometry (MS/MS) in centroid data

251

collection mode was performed. For both ion modes, the nebulization gas was set to 550 L h-1 at

252

a temperature of 250°C, the cone gas was set to 10 L h-1 and the source temperature was set to

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110°C. For negative-ion mode, the capillary and cone voltages were set to 2650 V and 25 V,

254

respectively and for positive-ion mode the capillary voltage was 3000 V and the cone voltage

255

was 35 V. For MS experiments, data were collected between m/z 20-1500 with collision energy

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of 8 eV and an acquisition rate of 0.4 sec spectrum-1. MS/MS experiments were performed by

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increasing the collision energy to 15-45 eV, specific to each analyte.

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Liquid chromatography quantitative analysis

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Sugars were separated and quantified using a Waters Acquity ultra performance liquid

261

chromatography (UPLC) system coupled to an evaporative light scattering detector (ELSD) and

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a Waters Micromass Q-Tof micro™ mass spectrometer (Waters Corp., Milford, MA). A Shodex

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Sugar SZ5532, 6 mm i.d. × 150 mm column (Showa Denko America Inc., New York, NY) was

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used at 65°C and a flow rate of 0.9 mL min-1 with a gradient of A) water and B) acetonitrile:

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starting with 20 % A; 9 min, 17% A; 25 min, 30% A; and lastly, 40 min, 40% A for a total run

266

time of 45 min. Sugars were monitored post-column, with the eluent flow split (2:1, v/v) to the

267

ELSD and the MS. Sugars were identified by positive-ion ESI/MS aided with a source


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temperature of 100°C, a capillary voltage of 3000 V with a nebulization gas of 550 L h-1 at a

269

temperature of 250°C, and a cone gas and voltage of 10 L h-1 and 25 V, respectively.

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Organic acids, select aldehydes, and select aldehydes were quantified via an Agilent 1100 HPLC

272

system fitted with a RID and a diode array (DAD) (Agilent Technologies, Santa Clara, CA).

273

Analytes were separated using an Aminex HPX-87H 9 µm, 7.8 mm i.d. × 300 mm column (Bio-

274

Rad Laboratories, Hercules, CA) using an isocratic mobile phase of 5 mM H2SO4 at a flow rate

275

of 0.6 mL min-1. Column and detector temperatures were maintained at 55°C.

276 277

Analysis of phenolic, aromatic, nitrogen-containing and larger molecular mass ketone

278

compounds was performed on an Agilent 1100 HPLC system equipped with a DAD and an Ion

279

Trap SL (Agilent Technologies, Santa Clara, CA) MS with in-line ESI. Each sample was

280

injected undiluted at a volume of 50 µL into the LC/MS system. Compounds were separated

281

using an YMC C30 Carotenoid 0.3 µm, 4.6 mm i.d. × 150 mm column (YMC America,

282

Allentown, PA) at an oven temperature of 30°C. The chromatographic eluents consisted of A)

283

water modified with 0.03% formic acid, and B) acetonitrile/water (9:1, v/v) also modified with

284

0.03% formic acid. At a flow rate of 0.7 mL min-1, the eluent gradient was as follows: 0-3 min,

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0% B; 16 min, 7% B; 21 min, 8.5% B; 34 min, 10% B; 46 min, 25% B; 51-54 min, 30% B; 61

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min, 50% B; and lastly 64-75 min, 100% B before equilibrium. Flow from the HPLC-DAD was

287

directly routed in series to the ESI-MS ion trap. The DAD was used to monitor chromatography

288

at 210 and 264 nm for a direct comparison to MS data. MS and MS/MS parameters are as

289

follows: smart parameter setting with target mass set to 165 Da, compound stability 70%, trap

290

drive 50%, capillary at 3500 V, fragmentation amplitude of 0.75 V with a 30 to 200 % ramped


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voltage implemented for 50 msec, and an isolation width of m/z 2 (He collision gas). The ESI

292

nebulizer gas was set to 60 psi, with dry gas flow of 11 L min-1 held at 350°C. Into each sample

293

and standard mixture, 0.01 g L-1 3,4-dihydroxybenzaldehyde (97% purity, Sigma Aldrich, St.

294

Louis, MO) was added to adjust for chromatographic shift and detector response. MS scans and

295

precursor isolation-fragmentation scans were performed across the range of 40-750 Da. All LC

296

quantitative analysis was performed in triplicate independent experiments (n=3) and all

297

quantitative standard curves were maintained with an R2 value of ≥ 0.995 with five or more

298

points of reference ranging between concentrations of 1 to 100 µg mL-1. Authentic standards

299

were obtained for quantitation in the highest purity available as listed in Table S3. Samples were

300

diluted with methanol accordingly to fit within the linear regions of the calibration curves. LC-

301

DAD/MS was also used to confirm the quantitation of many organic acids, sugars, furfural, and

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5-hydroxymethylfurfural as indicated in Table S2.

303 304

Gas chromatography quantitative analysis

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The aqueous fractions were diluted in methanol to fit within the linear range of calibration curves

306

prior to analysis by GC-MS for select ketone, aldehyde, and alcohol compounds. An Agilent

307

6890N gas chromatograph and Agilent 5973N mass-selective detector (Agilent Technologies,

308

Santa Clara, CA) was used for the identification of analytes. Using a splitless injection, 1 µL

309

sample volume was introduced onto a 30 m × 0.25 mm i.d., 0.25 µm film thickness DB-Wax

310

capillary column (J & W Scientific Inc., Folsom, CA) at 260°C. The helium flow was kept

311

constant at 1 ml min-1 with an oven program as follows: the initial column temperature of 35°C

312

was held for 3 min and then increased to 225°C at 5°C min-1 with a hold time of 1 min, and

313

lastly, to 250°C at 15°C min-1 with a hold time of 5 min. Electron impact ionization was used at


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70 eV electron energy and a mass scan range of m/z 25 – 450. An internal standard of 1,2-

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diphenylbenzene (99.9+% purity, AccuStandard, New Haven, CT) was added to all standards

316

and samples at a concentration of 0.05 g L-1 to adjust for any detector response shift. An Agilent

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Environmental ChemStation G1701DA version D.00.00.38 and NIST 2011 library was used for

318

data analysis. All gas chromatography quantitative analysis was performed in triplicate

319

independent experiments (n=3) and all quantitative standard curves ranged between 1 to 100 µg

320

mL-1 with no less than four points of reference and were maintained with a high correlations of

321

an R2 value of ≥0.995 Extracted ions specific to each analyte were used as quantitation markers

322

as presented in Table S2; additionally, GC-MS was used to confirm the quantitation of many

323

aldehydes, organic acids and aromatic compounds from LC analysis. Authentic standards were

324

obtained for quantitation in the highest purity available as listed in Table S3.

325 326

Results

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Efforts to characterize the organic matter from lignocellulosic biomass pyrolysis aqueous

328

streams focused on compositional and chemical characterization. Analysis was performed on the

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aqueous fractions of FP processes from NREL (FPNREL) and Stage Fraction 5 from ISU (SF5ISU),

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in addition to the aqueous fractions of CFP processes from NREL (CFPNREL ex situ), and RTI

331

International (CFPRTI-pine and CFPRTI-oak in situ). Samples from these streams are shown in Figure

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3.

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Figure 3. Aqueous FP and CFP streams studied in this work (from left) CFPNREL, CFPRTI-oak,

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CFPRTI-pine, SF5ISU, and FPNREL.

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Compositional characterization

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The physicochemical properties of the five aqueous streams are presented in Table 2 (with

340

deviations presented in Table S1). Unsurprisingly, given the differences in pyrolysis conditions

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and configurations, each process notably produced compositionally distinct fractions, further

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altered by feedstock selection, as seen between the RTI hardwood and softwood aqueous

343

streams. The water content ranged from 60 to 98 wt% between aqueous samples, indicating a

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considerable amount of organic and inorganic matter remaining in select aqueous fractions.

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Table 3 provides the inorganic composition of individual elements of the aqueous fractions

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measured on a dry weight basis. The total inorganics (wet weight basis) were 0.01 wt% FPNREL,

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0.01 wt% SF5ISU, 0.07 wt% CFPNREL, 0.01 wt% CFPRTI-pine, and 0.02 wt% CFPRTI-oak. The

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inorganic content of CFPNREL was likely high due to recent reactor commissioning, and a

349

reduction will be examined in further experiments. The inorganic composition accounted for a

350

minor fraction of the non-aqueous matter from the pyrolysis aqueous streams. The total organic

351

carbon (TOC) was measured to estimate organic matter content of each sample. Organic matter


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was determined using a conversion factor of 2.5, which was selected due to the low organic

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carbon content of the aqueous streams.24 Table 2. Physicochemical properties of pyrolysis aqueous streams Fast Pyrolysis Catalytic Fast Pyrolysis CFPNREL CFPRTI-pine CFPRTI-oak FPNREL SF5ISU ex-situ in-situ in-situ 80.6 59.6 97.5 86.4 93.9 Water (wt%) a 39.7 40.1 24.8 40.0 32.9 TOC (wt%) 105.1 188.3 105.1 87.0 24.3 TAN (mg NaOH g-1)a 5.9 9.6 42.8 12.0 5.5 Carbonyl (mmole g-1)a -1 a 765 808 1255 801 810 COD (mg g ) 2.3 2.1 1.6 2.8 5.3 pH a presented on a dry weight basis

354 Table 3. ICP-AES elemental analysis of pyrolysis aqueous streams presented in parts per million (ppm) on a dry weight basis Fast Pyrolysis Catalytic Fast Pyrolysis Element CFPRTI-pine CFPRTI-oak CFPNREL FPNREL SF5ISU (ppm) ex-situ in-situ in-situ 28.3 12.8 2887.0 76.1 94.1 Al 134.6 17.9 716.6 77.6 232.2 Ca

Aqueous Stream Characterization from Biomass ... - ACS Publications

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